Tears always flow out of the eyes, may be physiological reasons and pathological reasons, such as irritating gases, keratitis, dacryocystitis and so on. 1. Physiological reasons: cutting onions or eyes are subjected to some irritating gases, etc., there will always be tears flowing out of the eyes, usually leave the environment will gradually ease. 2. Pathologic causes: (1) Keratitis: the cornea is a relatively nerve-rich tissue, when inflammation occurs in keratitis, the inflammation may continue to stimulate the cornea causing tears. (2) Dacryocystitis: The narrowing of the nasolacrimal duct leads to an infection of the lacrimal sac, and when there is an increase in tear secretion caused by irritation of the eyes, frequent tearing may occur. Frequent tearing of the eyes, excluding physiological reasons, it is recommended to consult a doctor in a timely manner, follow the doctor’s instructions for further examination, with the help of the doctor to clarify the cause, and targeted treatment.